1. Field of the Disclosure
The present disclosure relates to an apparatus for wireless power transmission for transmitting power to portable electronic devices or small home appliances in a wireless manner to be used for charging a battery or operating the devices, and more particularly, to a wireless power transmission apparatus in which an antenna in charge of power transmission is configured as a multi antenna to optimize the power transmission efficiency for various devices which need charging.
2. Description of the Related Art
Portable electronic devices such as mobile communication terminals, PDA, PMP, and notebooks generally use rechargeable secondary batteries in order to enhance the convenience of users. By using such a battery as a driving power source, a user may become free of wired power supplies and thus use various products more conveniently.
A battery stores energy by being charged from an external power source, and a separate wired charging device is generally used for supplying a household power as a rated power useable for the battery in order to charge the battery.
Generally, in a wired charging method, a terminal of the charging device physically contacts a terminal of the battery for electric connection.
However, since the electric coupling is obtained by physical contact in the above method, the reliability of the connection may deteriorate due to physical abrasion. In addition, since the contact terminal tends to expose out, the contact state may become inferior due to contaminations caused by impurities. Moreover, in a moist or humid environment, problems such as an electric short circuit may occur or may easily lose the charged energy.
In order to solve the problems of the contact-type charging method, a non-contact charging system where a charging terminal does not physically contact the terminal of a battery is disclosed. The non-contact charging method uses the phenomenon that, if a magnetic flux in a magnetic field at a primary coil changes according to time, power is induced at a second coil adjacent thereto due to the magnetic field changing according to the time, as well known in the art.
FIG. 1 is a general schematic view showing a non-contact charging device and a battery using an induced electromotive force.
Referring to FIG. 1, a general non-contact charging device 10 includes a high frequency power generating unit 30 for receiving power from an AC power source 20 and outputting a high frequency AC current, and a primary coil 40 for receiving the high frequency AC current from the high frequency power generating unit 30 and forming a magnetic field M.
In addition, a battery 50 includes a battery cell 60 charged with an electric energy, a secondary coil 70 to which a high frequency AC current is induced according to the linkage of the magnetic field M generated at the primary coil 40, a rectifier 80 for converting the high frequency AC current induced at the secondary coil 70 into a DC current, and a constant-voltage/constant-current supplying unit 90 for applying the DC current rectified by the rectifier 80 to the battery cell 60. Here, the constant-voltage/constant-current supplying unit 90 is a circuit element widely used for battery charging devices. The constant-voltage/constant-current supplying unit 90 supplies a constant current to the battery cell 60 at an initial charging stage, and if the charging voltage of the battery cell 60 gradually increases and exceeds a specific reference value, the constant-voltage/constant-current supplying unit 90 maintains the voltage consistently, instead of decreasing the supplied current, until the battery cell 60 comes to a fully-charged state.
The general non-contact charging device 10 is configured by providing a wireless base pad including the primary coil 40 for generating an induced electromotive force, and placing a battery 50 having a secondary coil 70 corresponding to the primary coil 40 on the wireless base pad. However, in this configuration, the coil for generating the induced electromotive force should have a planar shape, and there is directivity between a power transmitting side and a power receiving side. Therefore, there is a limit in selecting the battery 50 which should be charged. For this reason, the charging efficiency may vary depending on the location of the battery 50 to be charged.
In addition, in the case where several devices require power to be charged, the general non-contact charging device 10 may additionally include a power converting module for transmitting power suitable for several devices, and the power converting module supplies power to several devices according to a control algorithm such as a time division control algorithm. However, although power may be transmitted to several devices requiring the same power, in order to charge several devices requiring different power, a complicated control algorithm should be considered. For this reason, power is unnecessarily wasted, which deteriorates the power transmission efficiency. In addition, in the case where the power converting module is designed to have a wide power conversion range, the efficiency of the power converting module deteriorates.